EP3899497B1 - Laser device for polarization interferometry - Google Patents

Description

The present invention generally relates to the field of interferometry and noise reduction in interferometers and other measuring devices derived from or coupled to interferometers such as ellipsometers or biosensors.

It is known to use interferometric devices for ellipsometric measurements, such as in the European patent EP1893977B1 or in the French patent FR2685962 . It is also known to use interferometric devices for surface plasmon resonance (SPR) measurements to detect molecular targets, for example in international patent applications WO2017153378 of the inventors of the present application and WO2009080998A2 , or the US patent US7233396B2 . These devices often implement bulky and expensive equipment, such as acousto-optic modulators, photo-elastic modulators, or Fresnel rhombohedrons.

• Aurélien Bruyant ET AL : « Interferometry Using Generalized Lock-in Amplifier (G-LIA): A versatile approach for Phase-Sensitive Sensing and Imaging" in "Optical Interferometry", 15 février 2017, InTech, XP55635442, pages 210-211 ;
• US 5305330A ;
• US 5374991 A ;

Watkins L R: "Novel interferometric ellipsometer with wavelength swept source", LASER AND ELECTRO-OPTICS, 2004 (CLEO), CONFERENCE ON SAN FRANCISCO, CA, USA, May 20-21, 2004, Piscataway, NJ, USA, IEEE, vol. 1, 17 mai 2004, pages 1043-1045, XP010745760 .The following documents relate to the field of the invention:

• Aurélien Bruyant ET AL: "Interferometry Using Generalized Lock-in Amplifier (G-LIA): A versatile approach for Phase-Sensitive Sensing and Imaging" in "Optical Interferometry", February 15, 2017, InTech, XP55635442, pages 210-211 ;
• US 5305330A ;
• US 5374991A ;

Watkins LR: "Novel interferometric ellipsometer with wavelength swept source", LASER AND ELECTRO-OPTICS, 2004 (CLEO), CONFERENCE ON SAN FRANCISCO, CA, USA, May 20-21, 2004, Piscataway, NJ, USA, IEEE, vol. 1, 17 May 2004, pages 1043-1045, XP010745760 .

In both cases, ellipsometric measurements or measurements by surface plasmon resonance, a high phase resolution is necessary in order to improve the sensitivity of the measurements. This high resolution can be provided by temporal modulation of the phase of the signals passing through the measurement devices. Indeed, an intrinsic advantage of the various systems with phase modulation compared to other systems for measuring stationary signals without a phase modulator is the noise reduction that allows a frequency analysis in the recovery of the amplitude and the phase, in particular thanks to the use of detections synchronous to the modulation frequencies of the detected interferometric signal. The US patent US5485271A describes an interferometric ellipsometer incorporating an electro-optical phase modulator. Other techniques allow phase modulation obtained by modulation of the birefringence of a component of the measuring device, such as those described in the American patent US7339681 B2 , where a liquid crystal cell is used, or in US patent US8004676B1 , where a photoelastic modulator is used. Also, a phase modulation can be obtained by modulation of the source beam wavelength, as in the international patent application WO2017/153378 , proposed by the present inventors, which describes a compact interferometer as well as a biochemical sensor derived therefrom, but which requires a particular optical chip producing two reflections, coming from two distant layers to carry out this modulation, which limits its application to samples particular and does not allow any optical excitation condition.

It is also known to use so-called common path interferometers, in which the reference beam and the signal beam linked to a sample move as much as possible along the same path, to reduce the noise of the interferometric measurements, due to the good immunity of this type of interferometer with respect to environmental vibrations.

It is also known to use asymmetric interferometers where the optical path difference between the two interfering arms is large enough for a low wavelength modulation of the light source used to cause a sufficient phase modulation to be able to extract an amplitude signal and a phase signal of the interferometric signal as explained by Valiant et al. in “An unbalanced interferometer insensitive to wavelength drift”. Sensors and Actuators A: Physical, 268, 188-192 (2017 ). In this type of device, however, the geometric path of the two beams is not common, thus limiting the stability of the system.

In addition, the drawback of the above-mentioned techniques lies in the size of their implementation device as well as in their cost, in order to obtain high accuracy and high measurement sensitivity. An interesting approach to minimize the noise of the interferometers consists in using a polarization interferometer which measures the phase difference between two orthogonal components of the field, because in this case the path followed by the two components of the field can be relatively common. Nevertheless, the phase modulation of one component with respect to the other requires an optical separation of the beams and a particular apparatus like those mentioned above, such as for example a photoelastic modulator.

The technical problem which the inventors propose to solve is to simplify the implementation and to improve the sensitivity of interferometric measuring devices of the polarization interferometer type, and the integration of this type of device both within ellipsometers than within SPR devices and to reduce their size and weight by avoiding the use of conventional active phase modulators and the use of moving parts to determine the state of the phase shift within said interferometer at polarization.

In order to solve this problem while overcoming the aforementioned drawbacks, the applicant has developed a laser device for polarization interferometry, suitable for delivering a temporally phase modulated laser beam according to claim 1.

Advantageously, the longitudinal single-mode laser source of the laser device can be a semiconductor laser whose wavelength can be modulated by the electric current supplying the laser over a range of tunability less than one thousandth of the wavelength. This low tunability is achieved by most consumer laser diodes.

Preferably, the semiconductor laser that can constitute the longitudinal monomode laser source of the laser device can be a laser diode with a vertical cavity emitting via the so-called VCSEL surface. However, in the absence of VCSEL, more widely tunable and typically more expensive lasers can be used.

Furthermore, the passive phase-retarding element of the laser device may comprise a birefringent crystal having an optical axis oriented along one of said polarization components TE or TM of the source laser beam S _source .

• un séparateur de faisceau de référence en sortie de l'élément retardateur de phase destiné à séparer le faisceau en au moins deux parties S_référence et S_modulé, la première partie S_référence étant une portion de référence du faisceau laser modulé temporellement en phase S_modulé, et ledit séparateur de faisceau étant configuré pour propager la portion de référence dans une direction différente de celle du faisceau laser modulé temporellement en phase S_modulé,
• un photo-détecteur de référence comprenant une entrée destinée à recevoir par l'intermédiaire d'un polariseur de référence ladite portion de référence S_référence, et ledit photo-détecteur de référence étant configuré pour générer un premier signal interférométrique, sous forme d'un premier signal électrique modulé I_ref représentatif de ladite portion de référence S_référence,
• une unité d'analyse électronique de référence configurée pour recevoir et analyser ledit signal électrique I_ref pour extraire un déphasage moyen Δ_ref entre les deux composantes orthogonales transverse électrique TE et transverse magnétique TM de la portion de référence S_référence,

• ledit signal électrique modulé I_ref représentatif de ladite portion de référence S_référence incluant un terme d'amplitude A_ref proportionnel au produit des amplitudes des deux composantes transverse électrique TE et transverse magnétique TM et un terme de phase,
• ladite unité d'analyse électronique de référence étant configurée pour, par analyse dudit signal électrique I_ref, extraire le déphasage moyen Δ_ref entre les deux composantes transverse électrique TE et transverse magnétique TM de la portion de référence S_référence, et extraire ledit terme d'amplitude A_ref, et
• l'unité d'analyse électronique de référence étant en outre configurée pour fournir un coefficient de correction au moyen de modulation temporelle de la source de sorte à ajuster la modulation temporelle de la source laser et à en stabiliser la longueur d'onde λ moyenne par stabilisation du déphasage moyen Δ_ref.

The laser device may further comprise:

• a reference beam splitter at the output of the phase delay element intended to separate the beam into at least two parts S _reference and S _modulated , the first part S _reference being a reference portion of the temporally modulated laser beam in phase S _modulated , and said beam splitter being configured to propagate the reference portion in a direction different from that of the _{modulated S-phase temporally modulated} laser beam,
• a reference photo-detector comprising an input intended to receive via a reference polarizer said reference portion S _reference , and said reference photo-detector being configured to generate a first interferometric signal, in the form of a first modulated electrical signal I _ref representative of said reference portion S _reference ,
• a reference electronic analysis unit configured to receive and analyze said electrical signal I _ref to extract an average phase shift Δ _ref between the two orthogonal transverse electrical TE and transverse magnetic TM components of the reference portion S _reference ,

• said modulated electrical signal I _ref representative of said reference portion S _reference including an amplitude term A _ref proportional to the product of the amplitudes of the two transverse electrical TE and transverse magnetic TM components and a phase term,
• said reference electronic analysis unit being configured to, by analysis of said electrical signal I _ref , extract the average phase shift Δ _ref between the two transverse electrical TE and transverse magnetic TM components of the reference portion S _reference , and extracting said amplitude term A _ref , and
• the reference electronic analysis unit being further configured to supply a correction coefficient to the source temporal modulation means so as to adjust the temporal modulation of the laser source and to stabilize the mean wavelength λ thereof by stabilization of the average phase shift Δ _ref .

Advantageously, said reference electronic analysis unit is connected to the time modulation means of the laser source so as to form a feedback loop to stabilize the average phase shift Δ _ref .

Optionally, to facilitate alignment, it may be useful to use beam splitters having reflective or anti-reflective treatments on different interfaces to avoid having multiple parasitic reflections. Other means can nevertheless be used alone or in addition to suppress the parasitic multiple reflections such as the use of non-parallel faces, and/or by spatially discriminating the first reflection and the first transmission, this including the use of thick blades.

The present application also proposes a polarization interferometer configured to measure characteristics of a sample, according to claim 7.

• un séparateur de faisceau de référence en sortie de l'élément retardateur de phase configuré pour séparer le faisceau en au moins deux parties S_référence et S_modulé, ladite partie S_référence étant une portion de référence du faisceau laser modulé temporellement en phase S_modulé, et étant configurée pour se propager dans une direction différente de celle du faisceau laser modulé temporellement en phase S_modulé,
• un photo-détecteur de référence comprenant une entrée configurée pour recevoir par l'intermédiaire d'un polariseur de référence ladite portion de référence S_référence, et ledit photo-détecteur de référence étant configuré pour générer un premier signal interférométrique, sous forme d'un premier signal électrique modulé I_ref représentatif de ladite portion de référence S_référence,
• une unité d'analyse électronique de référence configurée pour recevoir et analyser ledit signal électrique I_ref et déterminer Δ_échantillon et A_échantillon, alors l'incrément de déphasage optique Δ induit par l'échantillon est obtenu par la formule $$\Delta ={\Delta }_{\mathrm{échantillon}}-{\Delta }_{\mathrm{ref}}\mathrm{à}\mathrm{une}\mathrm{constante}\mathrm{additive}\mathrm{près}.$$
  

The modulated electrical signal I _sample representative of the output beam S _sample includes an amplitude term A _sample proportional to the product of the amplitudes of the two transverse electrical TE and transverse magnetic TM components of the output beam S _sample and a phase term Δ _sample including an optical phase shift increment Δ between the two transverse electric TE and transverse magnetic TM components induced by the sample. Consequently, the electronic analysis unit is configured to, by analyzing said electrical signal I _sample , extract said amplitude term A _sample and said mean phase term Δ _sample between the two transverse electrical TE and transverse magnetic TM components of the output beam S _sample making it possible to determine the optical characteristics of said sample. When the laser device further comprises:

• a reference beam splitter at the output of the phase delay element configured to split the beam into at least two parts S _reference and S _modulated , said part S _reference being a reference portion of the modulated laser beam temporally in phase S _modulated , and being configured to propagate in a direction different from that of the _{modulated S-phase temporally modulated} laser beam,
• a reference photo-detector comprising an input configured to receive via a reference polarizer said reference portion S _reference , and said reference photo-detector being configured to generate a first interferometric signal, in the form of a first modulated electrical signal I _ref representative of said reference portion S _reference ,
• a reference electronic analysis unit configured to receive and analyze said electrical signal I _ref and determine Δ _sample and A _sample , then the optical phase shift increment Δ induced by the sample is obtained by the formula $$\Delta ={\Delta }_{\mathrm{sample}}-{\Delta }_{\mathrm{ref}}\mathrm{To}a\mathrm{constant}\mathrm{additive}\mathrm{close}.$$
  

The present application also proposes an ellipsometer configured to determine an ellipsometric parameter Δ _ellipsometry of a sample, according to claim 9.

• un premier dispositif séparateur de faisceau sélectif en polarisation, configuré pour prélever une portion du faisceau de sortie S_échantillon et sélectionner une des deux composantes transverse électrique TE et transverse magnétique TM du faisceau de sortie S_échantillon sous la forme d'un faisceau S_tanΨ appelé portion polarisée,
• un photo-détecteur pour ellipsométrie complète configuré pour recevoir ladite portion polarisée S_tanΨ et générer un signal électrique I_tanΨ caractéristique de l'intensité lumineuse de la portion polarisée,

où ladite première voie de détection supplémentaire est configurée pour déterminer le paramètre ellipsométrique tanΨ de l'échantillon à l'aide des signaux électriques I_échantillon et I_tanΨ issus respectivement du photo-détecteur d'analyse et du photo-détecteur pour ellipsométrie complète.In a first variant of the proposed ellipsometer, the latter may also comprise a first additional detection channel, said first additional detection channel comprising:

• a first polarization-selective beam splitter device, configured to take a portion of the output beam S _sample and select one of the two transverse electric TE and transverse magnetic TM components of the output beam S _sample in the form of a beam S _tanΨ called polarized portion,
• a photo-detector for complete ellipsometry configured to receive said polarized portion S _tanΨ and generate an electrical signal I _tanΨ characteristic of the light intensity of the polarized portion,

where said first additional detection channel is configured to determine the ellipsometric parameter tanΨ of the sample using the electrical signals I _sample and I _tanΨ coming respectively from the analysis photo-detector and from the photo-detector for complete ellipsometry.

• un deuxième dispositif séparateur de faisceau sélectif en polarisation configuré pour prélever une portion du faisceau de sortie S_échantillon et sélectionner les deux composantes transverse électrique TE et transverse magnétique TM du faisceau de sortie S_échantillon sous la forme de deux faisceaux S_{tanΨ_TE} et S_{tanΨ_TM} appelés respectivement portion polarisée TE et portion polarisée TM,
• deux photo-détecteurs appelés photo-détecteur TE et photo-détecteur TM configurés pour recevoir respectivement lesdites portion polarisée TE S_{tanΨ_TE} et portion polarisée TM S_{tanΨ_TM} et pour générer respectivement un signal électrique I_{tanΨ_TE} caractéristique de l'intensité lumineuse de la portion polarisée TE S_{tanΨ_TE} et un signal électrique I_{tanΨ_TM} caractéristique de l'intensité lumineuse de la portion polarisée TM S_{tanΨ_TM},

dans lequel
la deuxième voie de détection supplémentaire est configurée pour déterminer le paramètre ellipsométrique tanΨ de l'échantillon à l'aide des signaux électriques I_{tanΨ_TE} et I_{tanΨ_TM} issus des photo-détecteur TE et photo-détecteur TM.In a second variant of the proposed ellipsometer, different from the first variant described above, the latter may also comprise a second additional detection channel, said second additional detection channel comprising:

• a second polarization-selective beam splitter device configured to take a portion of the output beam S _sample and select the two transverse electric TE and transverse magnetic TM components of the output beam S _sample in the form of two beams S _{tanΨ_TE} and S _{tanΨ_TM} called respectively TE polarized portion and TM polarized portion,
• two photo-detectors called photo-detector TE and photo-detector TM configured to respectively receive said polarized portion TE S _{tanΨ_TE} and polarized portion TM S _{tanΨ_TM} and to respectively generate an electrical signal I _{tanΨ_TE} characteristic of the light intensity of the polarized portion TE S _{tanΨ_TE} and an electrical signal I _{tanΨ_TM} characteristic of the light intensity of the polarized portion TM S _{tanΨ_TM} ,

in which
the second additional detection channel is configured to determine the ellipsometric parameter tanΨ of the sample using the electrical signals I _{tanΨ_TE} and I _{tanΨ_TM} from the photo-detector TE and photo-detector TM.

The present application also proposes a biosensor of the surface plasmon resonance detection system type configured to determine the characteristics of a sample consisting of a microfluidic layer MF, corresponding to the biological or biochemical medium to be analyzed, according to claim 12.

• La figure 1a illustre de manière schématique un premier mode de réalisation d'un dispositif laser tel que proposé ;
• La figure 1b illustre de manière schématique un deuxième mode de réalisation d'un dispositif laser tel que proposé ;
• La figure 2a illustre de manière schématique un premier mode de réalisation d'un interféromètre à polarisation tel que proposé ;
• La figure 2b illustre de manière schématique un deuxième mode de réalisation d'un interféromètre à polarisation tel que proposé ;
• La figure 3a illustre de manière schématique la partie nommée A d'un interféromètre à polarisation tel que proposé pour la mise en oeuvre d'une première variante d'un ellipsomètre pour ellipsométrie complète ;
• La figure 3b illustre de manière schématique la partie nommée A d'un interféromètre à polarisation tel que proposé pour la mise en oeuvre d'une deuxième variante d'un ellipsomètre pour ellipsométrie complète ;
• La figure 4a montre des résultats expérimentaux obtenus avec un ellipsomètre pour ellipsométrie complète ;
• La figure 4b montre des résultats expérimentaux obtenus avec un ellipsomètre pour ellipsométrie complète ;
• La figure 5 illustre de manière schématique la partie nommée A d'un interféromètre à polarisation tel que proposé pour la mise en oeuvre d'un biocapteur de type système de détection à résonance plasmon de surface ;
• La figure 6a montre des résultats expérimentaux obtenus avec un biocapteur de type système de détection à résonance plasmon de surface comme illustré sur la figure 5 ; et
• La figure 6b montre des résultats expérimentaux obtenus avec un biocapteur de type système de détection à résonance plasmon de surface comme illustré sur la figure 5.
• Les figures 1 à 6b sont commentées plus en détail au niveau de la description détaillée et des exemples qui suivent, qui illustrent l'invention sans en limiter la portée.

Other advantages and features of the present application will result from the following description, given by way of non-limiting example and made with reference to the appended figures:

• There picture 1a schematically illustrates a first embodiment of a laser device as proposed;
• There figure 1b schematically illustrates a second embodiment of a laser device as proposed;
• There figure 2a schematically illustrates a first embodiment of a polarization interferometer as proposed;
• There figure 2b schematically illustrates a second embodiment of a polarization interferometer as proposed;
• There picture 3a schematically illustrates the part named A of a polarization interferometer as proposed for the implementation of a first variant of an ellipsometer for complete ellipsometry;
• There figure 3b schematically illustrates the part named A of a polarization interferometer as proposed for the implementation of a second variant of an ellipsometer for complete ellipsometry;
• There figure 4a shows experimental results obtained with an ellipsometer for full ellipsometry;
• There figure 4b shows experimental results obtained with an ellipsometer for full ellipsometry;
• There figure 5 schematically illustrates the part named A of a polarization interferometer as proposed for the implementation of a biosensor of the surface plasmon resonance detection system type;
• There figure 6a shows experimental results obtained with a surface plasmon resonance detection system type biosensor as shown in the figure 5 ; And
• There figure 6b shows experimental results obtained with a surface plasmon resonance detection system type biosensor as shown in the figure 5 .
• THE figures 1 to 6b are commented on in more detail at the level of the detailed description and the examples which follow, which illustrate the invention without limiting its scope.

DETAILED DESCRIPTION

With reference to the picture 1a , a first embodiment of a laser device D comprises a longitudinal single-mode laser source 1. By longitudinal single-mode source is meant a laser source comprising a single mode, or a laser source essentially having a main longitudinal mode and possibly other longitudinal modes weak enough, in comparison, to be ignored or filtered out. The source is not necessarily transverse single mode, in the sense that a possibly complex field spatial distribution can be employed provided that the field can be considered as monochromatic. This laser source 1 is powered by an electrical supply current. The wavelength λ of the monomode laser source 1 is temporally modulated by a temporal modulation means 2. The source laser beam S _source coming from the laser source 1 comprises two non-zero orthogonal rectilinear polarization components called transverse electric, TE, and transverse magnetic, TM. The source laser beam S _source passes through a passive phase delay element 3 which introduces a phase shift between the TE and TM components of the source laser beam S _source . Due to the temporal modulation of the wavelength of the laser source 1, the phase difference between the TE and TM components is also temporally modulated. Thus, the beam coming from the passive phase delay element 3 is a _{modulated S-phase temporally modulated} laser beam. By phase-modulated laser beam is meant a laser beam in which the two polarization components are modulated relative to each other. In said device, the phase modulation can be achieved by maintaining a constant geometric path for the two components of the field and without an active modulation device other than the modulation of the laser source itself, the component where the modulation occurs being passive. .

To be more specific, when it is stated that phase modulation can be achieved by maintaining a constant geometric path for the two field components, it should be understood that the geometric path traveled by the two field components does not change in time, in particular at the level of the element where the phase shift occurs between these components, that is to say in the passive phase retarding element which is therefore fixed and advantageously monolithic for better stability.

Preferably, the laser source 1 is a semiconductor laser, for example a vertical cavity laser diode emitting through the VCSEL surface.

Furthermore, the temporal modulation of the wavelength of the laser source 1 can be carried out by temporally modulating the electrical supply current of the laser source 1. The temporal modulation of the wavelength of the laser source 1 is typically performed over a tunability range less than one thousandth of the wavelength. Thus, it is not necessary to resort to birefringence modulation or another type of modulator to cause this phase modulation between said components of the field.

In particular, the passive phase delay element 3 can for example comprise or consist of a component exhibiting birefringence, such as a birefringent crystal. In this particular case, the birefringent crystal advantageously has an optical axis along one of the two orthogonal transverse components of polarization of the source laser beam. Conventionally, these two polarization components are named TE and TM for "transverse electric" and "transverse magnetic" with reference to a certain plane of predetermined incidence. The geometric path followed by the components of the TE and TM field can then be entirely common. The phase modulation between the two components of the field is thus generated independently of the nature of any sample intercepting the beam, and of the optics used to excite the sample such as lenses, prisms or coupling gratings.

By common geometric path, it should be understood that the light beams of the TE and TM field components are spatially superimposed. Such a configuration allows, for example, a pooling of the noise undergone by the different beams, making the device more stable, this despite the difference in the optical paths traveled by the TE and TM components. It is recalled that the optical path is defined by the product of the refractive index encountered by the geometric path.

The optics used to excite the sample, mentioned in the previous paragraph, make it possible, for example, to define the angle(s) of incidence and more generally the lighting conditions on the sample. By the expression “exciting the sample”, it is understood to generate, using the laser device, an electromagnetic field, within the sample.

Various elements can also be added to this device, in particular with a view to stabilizing or even controlling the average phase shift existing between the two components of the field or more generally to controlling the state of polarization emanating from the laser device. In particular, with reference to the figure 1b , the laser device D may also have a reference arm comprising a reference beam splitter 4 which makes it possible to take from the output of the passive phase delay element 3 a reference portion of the modulated laser beam temporally _modulated in phase S, called S _reference , propagating in a direction other than that of the _{modulated S phase temporally modulated} laser beam. This reference portion S _reference is sent to a reference polarizer 5' through which the two components TE and TM of this reference portion S _reference interfere. Following its passage through the reference polarizer 5', the reference portion S _reference is intercepted by a reference photo-detector 5 which delivers a modulated electrical signal I _ref .

This modulated electrical signal I _ref is received and analyzed by a reference electronic analysis unit 6a. The modulated electrical signal I _ref includes an interferometric term modulated temporally in phase and having an amplitude A _ref proportional to the product of the amplitudes of the two transverse electrical TE and transverse magnetic TM components of the reference portion S _reference .

où

• E_TE et E_TM sont les amplitudes des composantes TE et TM de la portion de référence S_référence,
• M est un coefficient inférieur ou égal à 1, et $$A_{\mathit{<figure-callout\; id="2"\; label="ref"\; filenames="imgf0001.png"\; state="\{\{state\}\}">ref</figure-callout>}}^2=2{\mathit{mE}}_{\mathit{TE}}{E}_{\mathit{TM}},$$
  
  et
• Δ_mod est un terme de phase modulé temporellement, préférablement sinusoïdalement, mais pas nécessairement, suivant le choix de la fonction de modulation du courant. L'analyse de ce type de signal modulé I_ref est en particulier détaillée dans les références Al Mohtar, Abeer, et al. "Generalized lock-in détection for interferometry: application to phase sensitive spectroscopy and near-field nanoscopy." Optics express 22.18 (2014): 22232-22245 et le brevet US9518869B2 qui propose l'utilisation d'une détection synchrone modifiée dites détection synchrone généralisée pour effectuer l'analyse. L'emploi d'une détection synchrone généralisée permet effectivement d'extraire les informations d'amplitude A_ref et de phase Δ_ref , où Δ_ref caractérise dans notre cas le déphasage entre lesdites composantes TE et TM.

Indeed, the modulated electrical signal I _ref represents the interferometric signal detected by the reference photo-detector, which can be written in the form: $$I_{\mathit{ref}}<figure-callout\; id="2"\; label="\propto \; E\; YOU"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\propto </figure-callout>E_{\mathit{YOU}}^{}{\mathit{}}_2^{}+{\mathrm{<figure-callout\; id="2"\; label="E\; TM"\; filenames="imgf0001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathit{TM}}^{\mathit{}}+2{\mathit{me}}_{\mathit{YOU}}{E}_{\mathit{TM}}\mathit{cos}\left({\Delta }_{\mathit{mod}}+{\Delta }_{\mathit{ref}}\right)={\mathrm{<figure-callout\; id="2"\; label="E\; YOU"\; filenames="imgf0001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathit{YOU}}^{\mathit{}}+{\mathrm{<figure-callout\; id="2"\; label="E\; TM"\; filenames="imgf0001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathit{TM}}^{\mathit{}}+{\mathrm{<figure-callout\; id="2"\; label="AT\; ref"\; filenames="imgf0001.png"\; state="\{\{state\}\}">AT</figure-callout>}}_{\mathit{ref}}^{\mathit{}}\mathit{cos}\left({\Delta }_{\mathit{mod}}+{\Delta }_{\mathit{ref}}\right)$$

Or

• E _TE and E _TM are the amplitudes of the TE and TM components of the reference portion S _reference ,
• M is a coefficient less than or equal to 1, and $${\mathrm{AT}}_{\mathit{<figure-callout\; id="2"\; label="ref"\; filenames="imgf0001.png"\; state="\{\{state\}\}">ref</figure-callout>}}^2=2{\mathit{me}}_{\mathit{YOU}}{E}_{\mathit{TM}},$$
  
  And
• Δ _mod is a time-modulated phase term, preferably sinusoidally, but not necessarily, depending on the choice of the current modulation function. The analysis of this type of modulated signal I _ref is particularly detailed in the references Al Mohtar, Abeer, et al. "Generalized lock-in detection for interferometry: application to phase sensitive spectroscopy and near-field nanoscopy." Optics express 22.18 (2014): 22232-22245 and the patent US9518869B2 which proposes the use of a modified synchronous detection called generalized synchronous detection to carry out the analysis. The use of a generalized synchronous detection effectively makes it possible to extract the information of amplitude A _ref and of phase Δ _ref , where Δ _ref characterizes in our case the phase shift between said components TE and TM.

et $A_{\mathit{ref}}^2$

autour de leurs valeurs moyennes. Cette modulation supplémentaire peut fausser la mesure du déphasage si elle n'est pas prise en compte dans le traitement. Une détection synchrone généralisée, comme celle mentionnée, permet de traiter les signaux dont l'amplitude est également modulée temporellement et permet de s'affranchir de cette difficulté, idéalement en ajustant la profondeur de modulation de phase. A défaut, cette modulation sur lesdits termes d'intensité $E_{\mathit{TE}}^2$

, $E_{\mathit{TM}}^2$

et $A_{\mathit{ref}}^2$

peut être négligée au prix d'une certaine erreur, ou bien l'intensité I_ref mesurée peut être corrigée pour compenser cette modulation, connaissant la fonction de modulation utilisée. Le dispositif laser ainsi constitué est nommé D'.Thus, the reference electronic analysis unit 6a is capable of extracting from this electrical signal I _ref , comprising a phase-modulated interferometric term, the average phase shift Δ _ref between the two transverse electrical TE and transverse magnetic TM components of the portion of reference S _reference , and in extracting said amplitude term A _ref . This method thus makes it possible to extract said phase shift Δ _ref without ambiguity over its definition interval. In the absence of other extraction methods can be considered for particular temporal modulation functions, such as methods based on successive constant phase shifts, or the use of so-called serodyne ramp modulation. Particular attention should be paid to the fact that the current modulation also leads to a temporal modulation of the laser intensity, which leads to a modulation of the intensity terms. ${\mathrm{<figure-callout\; id="2"\; label="E\; YOU"\; filenames="imgf0001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathit{YOU}}^{\mathit{}},{\mathrm{<figure-callout\; id="2"\; label="E\; TM"\; filenames="imgf0001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathit{TM}}^{\mathit{}}$

And ${\mathrm{AT}}_{\mathit{<figure-callout\; id="2"\; label="ref"\; filenames="imgf0001.png"\; state="\{\{state\}\}">ref</figure-callout>}}^2$

around their mean values. This additional modulation can falsify the measurement of the phase shift if it is not taken into account in the processing. A generalized synchronous detection, such as that mentioned, makes it possible to process signals whose amplitude is also modulated temporally and makes it possible to overcome this difficulty, ideally by adjusting the depth of phase modulation. Otherwise, this modulation on said intensity terms $E_{\mathit{YOU}}^{}$${\mathit{}}_2^{}$

, ${\mathrm{<figure-callout\; id="2"\; label="E\; TM"\; filenames="imgf0001.png"\; state="\{\{state\}\}">E</figure-callout>}}_{\mathit{TM}}^{\mathit{}}$

And ${\mathrm{AT}}_{\mathit{<figure-callout\; id="2"\; label="ref"\; filenames="imgf0001.png"\; state="\{\{state\}\}">ref</figure-callout>}}^2$

can be neglected at the cost of a certain error, or else the intensity I _ref measured can be corrected to compensate for this modulation, knowing the modulation function used. The laser device thus formed is called D′.

In addition, by stabilizing the average phase shift Δ _ref , the reference electronic analysis unit 6a can supply a correction coefficient to the temporal modulation means 2 of the laser source 1 so as to adjust the temporal modulation of the laser source 1 and to stabilize its average wavelength λ. Thus, as indicated by the dotted line on the figure 1b , the reference electronic analysis unit 6a can be connected to the time modulation means 2 of the laser source so as to form a control loop to stabilize the average phase shift Δ _ref .

proportionnel au produit des amplitudes des deux composantes transverse électrique TE et transverse magnétique TM du faisceau de sortie S_échantillon, un terme de phase Δ_échantillon, et une modulation temporelle de la phase, c'est-à-dire du déphasage entre le deux composantes de polarisation. Outre la modulation temporelle de phase, ledit déphasage inclut un incrément de déphasage optique Δ entre les deux composantes transverse électrique TE et transverse magnétique TM qui est induit par l'échantillon 7 lors de la réflexion, transmission ou diffraction résultant de l'interaction avec l'échantillon, produites par un ou plusieurs composants optiques tels que des lentilles, des miroirs, ou réseaux, utilisés notamment en vue de convoyer la lumière sur l'échantillon solide, gazeux ou liquide dans les conditions d'illumination souhaitées par l'utilisateur. Mathématiquement, on peut traduire cette propriété par : $$I_{\mathit{échantillon}}\propto =I_0+A_{\mathit{échantillon}}^2\mathit{cos}\left({\Delta }_{\mathit{mod}}+{\Delta }_{\mathit{échantillon}}\right).$$

THE figures 2a and 2b illustrate two polarization interferometers, one, I, following the figure 2a , comprising a laser device D, and the other, I', according to the figure 2b , comprising a laser device D′. The interferometers I and I' comprise, in a part A at the output of the laser devices respectively D, or D', an opto-mechanical interface 70 illuminated by a temporally modulated laser beam in phase S _modulated coming from the laser device D, or D' , and transmitting the modulated S phase temporally _modulated laser beam towards a sample 7 of which it is desired to optically measure certain characteristics by the relative phase shift and possibly the relative attenuation that it induces between the two components of the field. The modulated S phase temporally _modulated laser beam then interacts with the sample 7 so as to generate an output beam S _sample which can be transmitted, reflected or even diffracted by the sample. At the output of the opto-mechanical interface 70, the _sample S output beam passes through an analysis polarizer 8' through which the two components TE and TM of the _sample S output beam interfere. Following its passage through the analysis polarizer 8', the output beam S _sample is intercepted by an analysis photo-detector 8 which delivers a modulated electrical signal I _sample representative of the interference between the two components TE and TM of the output beam S _sample . This modulated electric signal I _sample is received and analyzed by an electronic analysis unit 6b. In particular, the modulated electrical signal I _sample representative of the output beam S _sample includes a squared amplitude term ${\mathrm{AT}}_{\mathrm{<figure-callout\; id="2"\; label="e\; sample"\; filenames="imgf0001.png"\; state="\{\{state\}\}">e</figure-callout>}\mathit{sample}\mathit{}}^2$

proportional to the product of the amplitudes of the two transverse electric TE and transverse magnetic TM components of the output beam S _sample , a phase term Δ _sample , and a temporal modulation of the phase, that is to say of the phase shift between the two components of polarization. In addition to the temporal phase modulation, said phase shift includes an optical phase shift increment Δ between the two transverse electric TE and transverse magnetic TM components which is induced by the sample 7 during the reflection, transmission or diffraction resulting from the interaction with the sample, produced by one or more optical components such as lenses, mirrors, or gratings, used in particular to convey light onto the solid, gaseous or liquid sample under the illumination conditions desired by the user. Mathematically, we can translate this property by: $$I_{\mathit{sample}}\propto =I_0+{\mathrm{<figure-callout\; id="2"\; label="AT\; sample"\; filenames="imgf0001.png"\; state="\{\{state\}\}">AT</figure-callout>}}_{\mathit{sample}}^{\mathit{}}\mathit{cos}\left({\Delta }_{\mathit{mod}}+{\Delta }_{\mathit{sample}}\right).$$

Also in particular, the reference electronic analysis unit can be configured to, by analysis of said electric signal I _sample , extract said amplitude term A _sample and said average phase term Δ _sample between the two transverse electrical components TE and transverse magnetic TM of the output beam S _sample making it possible to determine the optical characteristics of said sample, specifically by means of the optical phase shift increment Δ, calculated, in the case where the interferometer is of type I', it is that is to say in the case where it comprises a laser device with reference arm D′, by: Δ=Δ _sample −Δ _ref to within an additive constant easily determinable, for example by calibration on a sample with a known Δ.

The type l' polarization interferometer illustrated in figure 2b can also be used as an ellipsometer operating in reflection or in transmission. In these two cases, a sample 7 is placed at the level of the interface 70 of the interferometer with polarization I′. The modulated S-phase _modulated laser beam, incident on the sample 7, is reflected specularly at the surface of the latter, or else is transmitted specularly by the latter for transmission, and propagates into an output beam S _sample intercepted by the analysis polarizer 8' and the analysis photo-detector 8. The electronic analysis unit 6b makes it possible, as explained above, to extract the ellipsometric parameter Δ _ellipsometry , by the formula Δ _ellipsometry + Δ _sample - Δ _ref up to an additive constant.

There picture 3a illustrates a first variant of the ellipsometer presented at the figure 2b , in which Part A includes additional elements described below. Indeed, in this first variant, the ellipsometer previously described further comprises a first additional detection channel making it possible to determine an ellipsometric parameter tanΨ of a sample 7. This additional channel comprises a first polarization-selective beam splitter device 9a in upstream of the analysis polarizer 8', which makes it possible to take a portion of the output beam S _sample and to filter one of the two transverse electric TE or transverse magnetic TM components of this portion of the output beam S _sample in the form of a S _tanΨ beam called polarized portion. This polarized portion S _tanΨ is intercepted by a photo-detector for complete ellipsometry 10 which generates an electrical signal I _tanΨ characteristic of the light intensity of the polarized portion. The ellipsometric parameter tanΨ of the sample is then determined using the quantities A _sample and I _tanΨ resulting respectively from the analysis of the signal I _sample resulting from the analysis photo-detector 8 and from the photo-detector for complete ellipsometry 10 .

• où r_TM et r_TE sont les coefficients de réflexion de l'échantillon portés par les composantes TM et TE du faisceau de sortie S_échantillon. Ainsi, le paramètre tanΨ peut être obtenu, suivant la configuration expérimentale utilisée, soit par son carré donné par l'équation : $${\left(\mathit{<figure-callout\; id="2"\; label="tan\psi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">tan\psi </figure-callout>}\right)}^2\propto \frac{A_{\mathit{échantillon}}^2}{I_{tan\mathrm{\Psi }}},$$
  
• si la composante TE est récupérée par la première voie de détection supplémentaire,
• soit par l'équation : $${\left(\mathit{<figure-callout\; id="2"\; label="tan\psi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">tan\psi </figure-callout>}\right)}^2\propto \frac{I_{tan\mathrm{<figure-callout\; id="2"\; label="\Psi \; A\; échantillon"\; filenames="imgf0001.png"\; state="\{\{state\}\}">\Psi </figure-callout>}}}{A_{\mathit{échantillon}}^{}}$$
  
• si la composante TM est récupérée par la première voie de détection supplémentaire.

Indeed, the parameter tanΨ is obtained, as classically in ellipsometry, by the formula: $$\mathit{tan\psi }=\left|\frac{r_{\mathit{TM}}}{r_{\mathit{YOU}}}\right|,$$

• where r _TM and r _TE are the sample reflection coefficients carried by the TM and TE components of the output beam S _sample . Thus, the parameter tanΨ can be obtained, depending on the experimental configuration used, either by its square given by the equation: $${\left(\mathit{<figure-callout\; id="2"\; label="tan\psi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">tan\psi </figure-callout>}\right)}^2\propto \frac{{\mathrm{AT}}_{\mathit{sample}}^2}{I_{\mathrm{you}\mathrm{To}\mathrm{not}\mathrm{\Psi }}},$$
  
• if the TE component is recovered by the first additional detection channel,
• either by the equation: $${\left(\mathit{<figure-callout\; id="2"\; label="tan\psi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">tan\psi </figure-callout>}\right)}^2\propto \frac{I_{\mathrm{you}\mathrm{To}\mathrm{not}\mathrm{\Psi }}}{{\mathrm{AT}}_{\mathit{<figure-callout\; id="2"\; label="sample"\; filenames="imgf0001.png"\; state="\{\{state\}\}">sample</figure-callout>}}^2}$$
  
• if the TM component is recovered by the first additional detection path.

There figure 4 presents tables of index and thickness measurements of samples of glass and silica on silicon obtained with an ellipsometer of the type of picture 3a .

There figure 3b illustrates a second variant of the ellipsometer presented at the figure 2b , in which Part A includes additional elements described below. Indeed, in this second variant, the ellipsometer previously described in figure 2b further comprises a second additional detection channel making it possible to determine an ellipsometric parameter tanΨ of a sample 7. This additional detection channel comprises a second polarization-selective beam splitter device 9b upstream of the analysis polarizer 8', which allows to take a portion of the output beam S _sample and to select the two transverse electric TE and transverse magnetic TM components of this portion of the output beam S _sample in the form of two beams S _{tanΨ_TE} and S _{tanΨ_TM} called respectively polarized portion TE and portion polarized TM and propagating in two different directions. The polarized portion TE and the polarized portion TM are each received respectively by a photo-detector 101 and a photo-detector 102, respectively called photo-detector TE and photo-detector TM. The ellipsometric parameter tanΨ of the sample is then determined using the electrical signals I _{tanΨ_TE} and I _{tanΨ_TM} from the photo-detector TE 101 and photo-detector TM 102.

There figure 5 schematically illustrates a biosensor of the surface plasmon resonance detection system type, comprising a laser device D and able to determine the characteristics of a sample consisting of an optical resonator ME interacting with a microfluidic layer MF, corresponding to the biological medium or biochemical to be analyzed 7. This biosensor comprises in a part A at the output of the laser device D (like the interferometer I described above), and receiving a temporally modulated laser beam in phase S _modulated , a removable biochip 11 which may comprise a prism 110 or more generally a coupling optic able to optically excite the sample formed by the optical resonator ME in interaction with the microfluidic layer MF representing the medium 7 to be analyzed. This biochip is positioned at an interface 70 and intercepts the modulated S phase temporally _modulated laser beam. This excites a surface plasmon resonance wave at the surface of the metal layer ME of the biochip, which interacts with the medium to be analyzed 7 at the level of the interface with the microfluidic layer before being reflected producing a beam S _sample . The output beam S _sample is intercepted by an analysis polarizer 8' followed by an analysis photo-detector 8 delivering an electrical signal I _sample . An electronic analysis unit 6b connected to the analysis photo-detector 8 makes it possible, as explained above, to determine the characteristics of said sample 7. The figures 6a and 6b illustrate the type of measurements that can be obtained with a biosensor as described previously and illustrated on the figure 5 . These figures will be described in more detail in the examples presented below.

EXAMPLES EXAMPLE 1: Implementation of a laser device

• source laser monomode longitudinal 1 : VCSEL référencé "VC670M-TO46GL" à 670 nm, d'accordabilité de l'ordre de 0.2nm/mA ;
• moyen de modulation temporelle électronique de la source laser 2 : modulation sinusoïdale du courant d'injection du VCSEL précité, de valeur moyenne i₀ suffisante par exemple égale à 4mA et de fréquence préférablement élevée pour réduire les bruits, jusqu'à 100kHz ou plus (suivant les capacités de l'électronique), exprimée par la relation i(t)=i₀+βsin(Ωt);
• élément retardateur de phase passif 3 : cristal de vanadate d'yttrium YVO4 de biréfringence égale à 0.22 et de longueur 10 mm ;
• séparateur de faisceau de référence 4 : lame séparatrice telle que la référence BSS04 (Thorlabs), ou cube séparateur ;
• polariseur de référence 5' : polariseur adapté à la longueur d'onde utilisée tel que LPVISE050-A (Thorlabs) ;
• photo-détecteur de référence 5 : photodétecteur adapté à la longueur d'onde utilisée et les fréquences de modulation employées, par exemple une photodiode en silicium pour le visible comme par exemple la référence PDA36A-EC (THORLABS) ;
• unité d'analyse électronique de référence 6a : carte d'acquisition électronique par exemple la référence NI USB-6363 (National Instrument).

A laser device is produced as illustrated in the figures 1a to 1b to implement a polarization interferometer which can be applied to a "complete" ellipsometric measurement or phase-sensitive SPR detection, and which makes it possible to determine the characteristics of a sample 7, for example of the thin or multilayer type such as treated glass , or samples used in micro-electronics, from the following elements:

• longitudinal single-mode laser source 1: VCSEL referenced "VC670M-TO46GL" at 670 nm, with a tunability of the order of 0.2 nm/mA;
• means of electronic temporal modulation of the laser source 2: sinusoidal modulation of the injection current of the aforementioned VCSEL, of average value i ₀ sufficient for example equal to 4mA and of preferably high frequency to reduce noise, up to 100 kHz or more ( depending on the capacities of the electronics), expressed by the relationship i(t)=i ₀ +βsin(Ωt);
• passive phase delay element 3: crystal of yttrium vanadate YVO4 with birefringence equal to 0.22 and length 10 mm;
• reference beam splitter 4: beam splitter such as reference BSS04 (Thorlabs), or splitter cube;
• 5' reference polarizer: polarizer adapted to the wavelength used, such as LPVISE050-A (Thorlabs);
• reference photodetector 5: photodetector adapted to the wavelength used and the modulation frequencies used, for example a silicon photodiode for the visible such as for example the reference PDA36A-EC (THORLABS);
• reference electronic analysis unit 6a: electronic acquisition card, for example the reference NI USB-6363 (National Instrument).

où Δl est la différence de chemin optique entre les deux composantes du champ au sein de l'élément retardateur 3. En pratique, il est intéressant de travailler avec une modulation de phase a= 3.83 rad comme expliqué dans un autre cadre par Vaillant et al. dans « An unbalanced interferometer insensitive to wavelength drift ». Sensors and Actuators A: Physical, 268, 188-192 . Dans la référence ci-dessus, ce choix de profondeur de modulation de phase permet d'analyser plus simplement le signal interférométrique résultant et d'extraire l'information d'amplitude A_échantillon et le terme de phase recherché Δ_échantillon simplement.The temporal modulation is typically performed by modulating the injection current of the longitudinal monomode laser source used. The modulation is preferably sinusoidal but other modulations can be used with a view to carrying out discrete or continuous phase shift interferometric detection. In the sinusoidal case, the modulation of the injection current i(t) is, as mentioned, of the type: i ₀ +βsin(Ωt). In the case of the aforementioned type of VCSEL, i ₀ is typically of the order of 4 mA. The current modulation induces an optical power modulation approximately equal to: P(t)=P ₀ +γsin(Ωt)=P ₀ (1+µsin(Ωt)), where P ₀ is the DC power component, and µ *P ₀ , the AC amplitude of the modulation, Ω is the pulse of the modulation. This power modulation induces a wavelength modulation approximately equal to λ(t)=λ ₀ +δsin(Ωt), where λ ₀ is the average wavelength and δ is the wavelength modulation depth. In the presence of such modulation (of current, but also of power and wavelength), a phase modulation is created between the TE and TM components as soon as the beam passes through the birefringent crystal YVO4 mentioned above. The induced phase modulation is written: asin(Ωt) in the sinusoidal case, with the phase modulation depth given by: $$\mathrm{To}=\frac{4\mathit{<figure-callout\; id="0"\; label="\pi \Delta l\delta \; \lambda "\; filenames="imgf0005.png"\; state="\{\{state\}\}">\pi \Delta l\delta </figure-callout>}}{{\lambda }_{}^{}},$$

where Δ l is the optical path difference between the two components of the field within the delay element 3. In practice, it is advantageous to work with a phase modulation a=3.83 rad as explained in another context by Valiant et al. in “An unbalanced interferometer insensitive to wavelength drift”. Sensors and Actuators A: Physical, 268, 188-192 . In the above reference, this choice of phase modulation depth makes it easier to analyze the resulting interferometric signal and to extract the amplitude information A _sample and the phase term sought Δ _sample simply.

In our case, to obtain the temporal phase modulation, the birefringence (n _e -n _o ) and the length L of the YVO4 crystal are such that the optical path difference given by the product L(n _e -n _o ) is at minimum of the order of magnitude of a millimeter, which corresponds to a cumulative phase shift between the TM component and the TE component of the order of 10,000 radians for visible light. This cumulative optical path difference is achieved with the previously mentioned components.

EXAMPLE 2: Measurement of a parameter Δ _ellipsometry

An ellipsometer is produced as described previously and illustrated in figure 2b to determine a parameter Δ _ellipsometry , from the laser device described in example 1.

• une interface opto-mécanique 70 configurée pour transmettre le faisceau laser modulé temporellement en phase S_modulé sortant du dispositif laser selon l'exemple 1 vers un échantillon 7 de sorte que le faisceau laser modulé temporellement en phase S_modulé interagisse avec l'échantillon de façon à générer un faisceau de sortie S_échantillon;
• un polariseur d'analyse 8' : polariseur LPVISE050-A (Thorlabs) ;
• un photo-détecteur d'analyse 8 : photodiode en silicium par exemple la référence PDA36A-EC (THORLABS) ;
• une unité d'analyse électronique 6b : carte d'acquisition électronique par exemple la référence NI USB-6363 (National Instrument).

To implement the aforementioned ellipsometer, the following are also used:

• an opto-mechanical interface 70 configured to transmit the modulated S-phase temporally _modulated laser beam emerging from the laser device according to example 1 to a sample 7 so that the modulated laser beam temporally in-phase _modulated S interacts with the sample to generate a _sample S output beam;
• an 8' analysis polarizer: LPVISE050-A polarizer (Thorlabs);
• an analysis photo-detector 8: silicon photodiode, for example the reference PDA36A-EC (THORLABS);
• an electronic analysis unit 6b: electronic acquisition card, for example the reference NI USB-6363 (National Instrument).

The ellipsometric parameter Δ _ellipsometry is obtained by the formula Δ _ellipsometry =Δ _sample -Δ _ref up to an additive constant, with Δ _sample the phase parameter extracted from the electrical signal I _sample coming from the analysis photo-detector 8, and corresponding to the phase shift between the TE and TM components of the output beam S _sample induced by the sample.

EXAMPLE 3: Ellipsometric measurements of indices and thicknesses of samples of multilayers of the thin film type

• un premier dispositif séparateur de faisceau sélectif en polarisation 9a, séparateur simple tel BSS04 (Thorlabs) suivi de polariseurs tels LPVISE050-A (Thorlabs) ;
• un photo-détecteur pour ellipsométrie complète 10.

An ellipsometer is made as shown in picture 3a to determine parameters Δ _ellipsometry and tanΨ, from the ellipsometer described in example 2, and further comprising:

• a first polarization-selective beam splitter device 9a, simple splitter such as BSS04 (Thorlabs) followed by polarizers such as LPVISE050-A (Thorlabs);
• a photo-detector for complete ellipsometry 10.

, si la composante TE est récupérée par la première voie de détection supplémentaire, ou l'inverse si la composante TM est récupérée par la première voie de détection supplémentaire. En pratique, le coefficient de proportionnalité entre (tanΨ)² et A² _échantillon/I_tanΨ peut être prédéterminé simplement par une expérience de calibration sur un échantillon connu. Dans cet exemple, le coefficient de proportionnalité est préalablement déterminé en mesurant le paramètre tanΨ sur un échantillon connu.The ellipsometric parameter Δ _ellipsometry is obtained as in example 2. The parameter (tan _Ψ ) ² can be obtained, depending on the experimental configuration used, either by the equation ${\left(\mathit{tan\psi }\right)}^{}$${\left(\mathit{}\right)}^2\propto \frac{{\mathrm{AT}}_{\mathrm{e}\mathit{sample}}^2}{I_{\mathrm{you}\mathrm{To}\mathrm{not}\mathrm{\Psi }}}$

, if the TE component is recovered by the first additional detection channel, or the reverse if the TM component is recovered by the first additional detection channel. In practice, the proportionality coefficient between (tanΨ) ² and A ² _sample /I _tanΨ can be predetermined simply by a calibration experiment on a known sample. In this example, the proportionality coefficient is determined beforehand by measuring the parameter tanΨ on a known sample.

From the parameters _{Δellipsometry} and tanΨ, it is possible to determine, as conventionally in ellipsometry, the complex optical index or the thickness of the known thin layer or other unknown parameters linked for example to the roughness. There figure 4 illustrates a set of experimental results obtained with the ellipsometer previously described.

EXAMPLE 4: Ellipsometric measurements of indices and thicknesses of samples of the thin layers or multilayer stacks type

• un deuxième dispositif séparateur de faisceau sélectif en polarisation 9b : séparateur simple tel BSS04 (Thorlabs) suivi de polariseurs tels LPVISE050-A (Thorlabs), ou séparateurs simples fonctionnant en incidence Brewsterienne ;
• deux photo-détecteurs 101 et 102 : photodiodes en silicium, éventuellement amplifiées, par exemple la référence PDA36A-EC (THORLABS).

An ellipsometer is made as shown in figure 3b to determine parameters Δ _ellipsometry and tanΨ, from the ellipsometer described in example 2, and further comprising:

• a second polarization-selective beam splitter device 9b: single splitter such as BSS04 (Thorlabs) followed by polarizers such as LPVISE050-A (Thorlabs), or single splitters operating at Brewsterian incidence;
• two photo-detectors 101 and 102: silicon photodiodes, possibly amplified, for example the reference PDA36A-EC (THORLABS).

avec I_{tanΨ_TE} et I_{tanΨ_TM} les signaux issus des photo-détecteur TE et photo-détecteur TM. Le coefficient de proportionnalité est égal à l'unité si les faisceaux sont partagés en proportions identiques. En pratique le coefficient peut être prédéterminé simplement par une expérience de calibration, par exemple sur un échantillon connu. A partir des paramètres Δ_{ellipsométrie} et tanΨ, il est possible de déterminer, comme classiquement en ellipsométrie, l'indice complexe et l'épaisseur de couches au sein de l'échantillon mesuré.The ellipsometric parameter Δ _ellipsometry is obtained as in examples 2 and 3. As described above, the parameter tanΨ is directly obtained by its square: $${\left(\mathit{<figure-callout\; id="2"\; label="tan\psi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">tan\psi </figure-callout>}\right)}^2\propto \frac{I_{\mathrm{you}\mathrm{To}\mathrm{not}\mathrm{\Psi }\_\mathrm{TM}}}{I_{\mathrm{you}\mathrm{To}\mathrm{not}\mathrm{\Psi }\_\mathrm{YOU}}}$$

with I _{tanΨ_TE} and I _{tanΨ_TM} the signals coming from the photo-detector TE and photo-detector TM. The proportionality coefficient is equal to unity if the beams are shared in identical proportions. In practice, the coefficient can be predetermined simply by a calibration experiment, for example on a known sample. From the parameters _{Δellipsometry} and tanΨ, it is possible to determine, as conventionally in ellipsometry, the complex index and the thickness of layers within the measured sample.

EXAMPLE 5 Surface plasmon resonance type measurements and detection of thiolated PEG (poly-ethylene glycol-SH)

• une interface opto-mécanique 70 : support ;
• un polariseur d'analyse 8' : polariseur LPVISE050-A (Thorlabs) ;
• un photo-détecteur d'analyse 8 : photodiode en silicium par exemple la référence PDA36A-EC (THORLABS) ;
• une unité d'analyse électronique 6b : carte d'acquisition électronique par exemple la référence NI USB-6363 (National Instrument) ;
• la biopuce préférablement amovible 11 disposée sur l'interface 70 et comprenant un prisme 110 sur lequel est déposée une couche métallique ME d'or (d'épaisseur 45nm) apte à recevoir la couche PEG thiolé constituant l'échantillon à analyser.

A biosensor is produced as illustrated in the figure 5 for application to surface plasmon resonance type detection making it possible to measure parameters of a sample 7 in order to monitor here the deposition of thiolated PEG thereon. The sample consists of an optical resonator (ME) formed here of a gold layer of about 45nm interacted with the solution containing the thiolated PEG (poly-ethylene glycol-SH) present within the microfluidic layer . This biosensor illustrated on the figure 5 is made from the laser device described in example 1, adding to it as illustrated in the figure 5 :

• an opto-mechanical interface 70: support;
• an 8' analysis polarizer: LPVISE050-A polarizer (Thorlabs);
• an analysis photo-detector 8: silicon photodiode, for example the reference PDA36A-EC (THORLABS);
• an electronic analysis unit 6b: electronic acquisition card, for example the reference NI USB-6363 (National Instrument);
• the preferably removable biochip 11 placed on the interface 70 and comprising a prism 110 on which is deposited a metallic layer ME of gold (thickness 45 nm) capable of receiving the thiolated PEG layer constituting the sample to be analyzed.

In this specific case, the analysis photo-detector 8 is an imager allowing multipoint measurement. The biosensor is used in the so-called Kretschmann configuration via the prism (110). The parameter Δ=Δ _sample −Δ _ref which can be determined thanks to the polarization interferometer of the biosensor as described above is generally not accessible with other types of SPR measurement devices. There figure 6a illustrates the measurement of the functionalization of the gold layer in contact with the microfluidic layer of thiolated PEG. This type of measurement makes it possible to obtain optogeometric information on the deposited layer and here in particular to know the time at the end of which the reaction only changes slightly (eg 3500 seconds).

EXAMPLE 6: Surface plasmon resonance type measurements and detection of different amounts of 40 mer DNA

There figure 6b illustrates measurements aimed at detecting different amounts of DNA binding to the surface (phase sensorgrams), via the variations of the parameter Δ over time within the different regions of interest. The comparison with the reference signals makes it possible to overcome fluctuations in the parameters amplitude and phase unrelated to the target itself, such as environmental variations such as temperature variations at the level of the chip itself. The microfluidic layer used here is composed of complementary DNA strands of 40 mer codons. The curves of different color levels (black to light gray) thus show a kinetics of variation characteristic of the concentrations analyzed, here from 25 nM to 500 nM. The curves observed follow a conventional adsorption process of the isothermal Langmuir type.

It should be noted that the SPR type measurements above, carried out with a laser device according to example 1, can also be carried out using a laser device as proposed in the present application having other characteristics. , for example, with a laser source operating at a completely different wavelength, such as in the mid-infrared or near-infrared, for example with a VCSEL operating at a wavelength of about 850 mm with the same modulation of phase, or 3.84rad, and adapting the current modulation in mA to achieve this phase modulation, as well as the system components to operate at this wavelength.

Other embodiments can be considered. For example, another embodiment may include multi-angle measurements, where, in both cases of applications to ellipsometry or surface plasmon resonance detection, measurements at several angles of incidence are performed, or conversely, the beam at the output of the measured sample is separated after interaction with the sample at several different angles. In the case of the plurality of angles of incidence, a cylindrical lens can for example be placed upstream of the interface receiving the samples to be tested to obtain a focused beam in the plane of incidence, thus giving a plurality of angles of incidence illuminating the sample, the latter reflecting the extended beam received in several directions picked up by a linear detector (of the diode array type for example).

Also, as mentioned in example 6, the analysis photo-detectors 8, photo-detector for complete ellipsometry 10, and TE photo-detector and TM photo-detector 101 and 102 can be two-dimensional sensors making it possible to image samples to be measured and to obtain two-dimensional maps of the characteristics of these samples. In this case, all types two-dimensional sensors can be used, such as CCD or CMOS sensors, or photodetectors having a reduced number of detection zones such as quadrant photodiodes which can also help in centering the beam.

Also, ellipsometric measurements in transmission can be carried out in the case of sufficiently transparent samples. A plurality of laser optical sources can also be employed to extend the spectral domain of analysis. Also, the ellipsometric analysis can be extended to obtain additional information on the sample from the ellipsometric parameters determined from a model that can take into account in particular the density or the roughness of a layer.

Also, the SPR device being able to integrate an ellipsometric measurement, the latter can be used to determine the characteristics of the layers making up the biochip, for example the thickness of the gold deposit, or the thickness (or the density) of a layer of functionalization, or even the molecular layers resulting from the analyte crossing the microfluidic layer clinging to the surface. Thus the biochip can be prepared for the measurement of any biochemical species (pathogens, proteins, bacteria, biomarkers) using the ellipsometric measurement device at each step of the functionalization process, which is typically carried out on SPR biochips to allow the detection of a target in particular using antibodies, DNA or aptamers.

The examples of optomechanical interfaces 70 given in this description are not limiting. Thus, in addition to a simple support as in example 5, or a coupling prism provided or not with a resonant element as in example 5, coupling gratings or lenses could be used to optically excite a sample resonance. In particular, SPR devices typically require a coupling element as in the examples given in this description. The coupling element makes it possible to obtain, if necessary, a plurality of excitation angles. The preferred excitation of SPR devices is excitation at a supercritical angle known as the Kretschmann configuration. Thus the essential role of the opto-mechanical interface is to define the angle(s) of incidence and more generally the lighting conditions on the sample.

Claims (12)

1. A laser device (D) for polarization interferometry adapted to deliver a temporally phase-modulated laser beam (S_modulated) and comprising:

   - a longitudinal single-mode laser source (1), powered by an electrical power supply current, and configured to deliver a polarized source laser beam (S_source) of wavelength (λ), comprising two non-zero orthogonal rectilinear polarization components, respectively called electric transverse, TE, and magnetic transverse, TM,

   - means for electronic temporal modulation of the laser source (2) configured to drive a temporal modulation of the wavelength of the source laser beam (S_source),

   - a passive phase delay element, producing two paths of different optical lengths for said TE and TM polarization components (3), configured to receive the source laser beam (S_source) and to introduce, due to the wavelength modulation of the source laser beam (S_source), a temporally modulated phase shift between said TE and TM components to provide said temporally phase-modulated laser beam (S_modulated), wherein the passive phase delay element comprises a component having a birefringence and is configured to create a common geometric path for the TE and TM components.
2. The laser device (D) according to claim1 , wherein the laser source (1) is a semiconductor laser which can be wavelength-modulated by the electrical current for powering the laser over a tunability range of less than one thousandth of the wavelength.
3. The laser device (D) according to claim 2, wherein the semiconductor laser type source (1) is a vertical-cavity surface-emitting laser diode VCSEL.
4. The laser device (D) according to claim 3, wherein the phase delay element (3) comprises a birefringent crystal having an optical axis oriented along one of said TE or TM polarization components of the source laser beam (S_source).
5. The laser device (D') according to one of claims 1 to 4, further comprising:

   - a reference beam splitter (4) at the output of the phase delay element (3) intended to split the beam into at least two portions (S_reference) and (S_modulated), the first portion (S_reference) being a reference portion of the temporally phase-modulated laser beam (S_modulated), and said beam splitter being configured to propagate the reference portion in a direction different from that of the temporally phase-modulated laser beam (S_modulated)

   - a reference photo-detector (5) comprising an input intended to receive, via a reference polarizer (5'), said reference portion (S_reference), and said reference photo-detector (5) being configured to generate a first interferometric signal, in the form of a first modulated electrical signal (I_ref) representative of said reference portion (S_reference)

   - a reference electronic analysis unit (6a) configured to receive and analyze said electrical signal (I_ref) to extract an average phase shift (Δ_ref) between the two electric transverse TE and magnetic transverse TM orthogonal components of the reference portion (S_reference), the modulated electrical signal (I_ref) representative of said reference portion (S_reference) including an amplitude term (A_ref) proportional to the product of the amplitudes of the two electric transverse TE and magnetic transverse TM components and a phase term,

   the reference electronic analysis unit (6a) being configured to, by analysis of said electrical signal (I_ref), deduce therefrom the average phase shift (Δ_ref) between the two electric transverse TE and magnetic transverse TM components of the reference portion (S_reference), and to extract said amplitude term (A_ref), and

   the reference electronic analysis unit (6A) being further configured to provide a correction coefficient to the means for temporal modulation of the laser source (2) so as to adjust the temporal modulation of the laser source (1) and to stabilize the average wavelength λ thereof by stabilization of the average phase shift (Δ_ref).
6. The laser device (D') according to claim 5, wherein said reference electronic analysis unit (6a) is connected to the means for temporal modulation of the laser source (2) so as to constitute a servo-control loop for stabilizing the average phase shift (Δ_ref).
7. A polarization interferometer I configured to measure characteristics of a sample (7), comprising:

   - a laser device (D) or (D') according to any one of claims 1 to 6, adapted to deliver a temporally phase-modulated laser beam (S_modulated);

   - an opto-mechanical interface (70):

   - an analysis photo-detector (8) and an analysis polarizer (8');

   - an electronic analysis unit (6b);

   wherein

   said opto-mechanical interface (70) being a simple support of the sample or an optical coupling system, which can include different optics, configured to receive and transmit the temporally phase-modulated laser beam (S_modulated) toward the sample (7) so as to generate an output beam (S_sample),

   the analysis photo-detector (8) comprises an input configured to receive, via the analysis polarizer (8'), said output beam (S_sample), and said analysis photo-detector (8) being configured to generate a second interferometric signal, in the form of a second modulated electrical signal (I_sample),

   said electronic analysis unit (6b) is connected to the analysis photo-detector (8) and is configured to receive and analyze said modulated electrical signal (I_sample) to determine characteristics of said sample (7).
8. The polarization interferometer I according to claim7, configured to determine optical characteristics of said sample (7), wherein the electronic analysis unit (6b) is configured to, by analysis of said electrical signal (I_sample), extract an amplitude term (A_sample) and an average phase term (Δ_sample) between the two electric transverse TE and magnetic transverse TM components of the output beam (S_sample) allowing determination of the optical characteristics of said sample (7), and

   when the polarization interferometer comprises:

   - a reference beam splitter (4) at the output of the phase delay element (3) configured to split the beam into at least two portions (S_reference) and (S_modulated), said portion (S_reference) being a reference portion of the temporally phase-modulated laser beam (S_modulated), and being configured to propagate in a direction different from that of the temporally phase-modulated laser beam (S_modulated),

   - a reference photo-detector (5) comprising an input configured to receive, via a reference polarizer (5'), said reference portion (S_reference), and said reference photo-detector (5) being configured to generate a first interferometric signal, in the form of a first modulated electrical signal (I_ref) representative of said reference portion (S_reference),

   - a reference electronic analysis unit (6a) configured to receive and analyze said electrical signal (I_ref),

   said reference electronic analysis unit (6a) is further configured to extract an average phase shift (Δ_ref) between the two electric transverse TE and magnetic transverse TM components of the reference portion (S_reference), so as to calculate, to within an additive constant, an optical phase shift increment (Δ) induced by the sample by the formula Δ=Δ_sample- Δ_ref.
9. An ellipsometer configured to operate in reflection, and configured to determine an ellipsometric parameter (Δ_ellipsometry) of a sample (7) comprising a polarization interferometer I according to claim 8 and wherein:

   the opto-mechanical interface (70) of the polarization interferometer (I) is able to receive the sample (7),
   and

   when the laser device is a laser device D', comprising:

   - a reference beam splitter (4) at the output of the phase delay element (3) configured to split the beam into at least two portions (S_reference) and (S_modulated), said portion (S_reference) being a reference portion of the temporally phase-modulated laser beam (S_modulated), and being configured to propagate in a direction different from that of the temporally phase-modulated laser beam (S_modulated),

   - a reference photo-detector (5) comprising an input configured to receive, via a reference polarizer (5'), said reference portion (S_reference), and said reference photo-detector (5) being configured to generate a first interferometric signal, in the form of a first modulated electrical signal (I_ref) representative of said reference portion (S_reference),

   - a reference electronic analysis unit (6a) configured to receive and analyze said electrical signal (I_ref), then

   the reference electronic analysis unit (6a) is configured, by analysis of said electrical signal (I_ref), to extract an average phase shift (Δ_ref) between the two electric transverse TE and magnetic transverse TM components of the reference portion (S_reference), to obtain the ellipsometric parameter (Δ_ellipsometry) by the formula (Δ_ellipsometry) = (Δ_sample▪ (Δ_ref) to within an additive constant.
10. The ellipsometer according to claim 9, configured to determine an ellipsometric parameter (tan_Ψ) of a sample (7) and comprising a first additional detection channel, said first additional detection channel comprising:

    - a first polarization-selective beam splitter device (9a), configured to take a portion of the output beam (S_sample) and select one of the two electric transverse TE and magnetic transverse TM components of the output beam (S_sample) in the form of a beam (S_tanΨ) called polarized portion

    - a photo-detector for complete ellipsometry (10) configured to receive said polarized portion (S_tanΨ) and to generate an electrical signal (I_tanΨ) characteristic of the light intensity of the polarized portion, where said first additional detection channel is configured to determine the ellipsometric parameter (tan_Ψ) of the sample using the electrical signals (I_sample) and (I_tanΨ) respectively from the analysis photo-detector (8) and the photo-detector for complete ellipsometry (10).
11. The ellipsometer according to claim 9, configured to determine an ellipsometric parameter (tan_Ψ) of a sample (7) and further comprising a second additional detection channel, said second additional detection channel comprising:

    - a second polarization-selective beam splitter device (9b) configured to take a portion of the output beam (S_sample) and select the two electric transverse TE and magnetic transverse TM components of the output beam (S_sample) in the form of two beams (S_{tanΨ_TE}) and (S_{tanΨ_TM}) called TE polarized portion and TM polarized portion, respectively,

    - two photo-detectors (101) and (102) called TE photo-detector and TM photo-detector configured to receive said TE polarized portion (S_{tanΨ_TE}) and TM polarized portion (S_{tanΨ_TM}), respectively, and to generate a respective electrical signal (I_{tanΨ_TE}) characteristic of the light intensity of the TE polarized portion (S_{tanΨ_TE}) and an electrical signal (It_{anΨ_TM}) characteristic of the light intensity of the TM polarized portion (S_{tanΨ_TM}), where the second additional detection channel is configured to determine the ellipsometric parameter (tan_Ψ) of the sample using the electrical signals (I_{tanΨ_TE}) and (I_{tanΨ_TM}) from the TE photo-detector (101) and TM photo-detector (102).
12. A biosensor of the surface plasmon resonance detection system type configured to determine characteristics of a sample (7) consisting of a microfluidic layer (MF), corresponding to the biological or biochemical medium to be analyzed, the biosensor comprising:

    - a polarization interferometer (I) according to any one of claims 7 or 8 or an ellipsometer according to any one of claims 9 to 11

    - a removable biochip (11), which is supported by a prism, on which is deposited a thin resonant metal layer or another optical resonator (ME) capable of receiving the microfluidic layer (MF) to be analyzed by said polarization interferometer or said ellipsometer, said biochip being configured so as to intercept the temporally phase-modulated laser beam (S_modulated) wherein:

    - the interaction between the temporally phase-modulated laser beam (S_modulated) and the sample consists of a resonant optical excitation of the resonator (ME) of the biochip in interaction with the microfluidic layer (MF), producing said output beam (S_sample)

    - said output beam (S_sample) characteristic of the sample (7) is configured to be sensed by the analysis photo-detector (8)

    - the electronic analysis unit (6b) is configured to analyze said modulated electrical signal (I_sample) representative of the output beam (S_sample) generated by the analysis photo-detector (8) in order to determine characteristics of said sample (7).

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